A liquid crystal display device gas been widely utilized for a display of a personal computer, television or the like. The device utilizes optical anisotropy, dielectric anisotropy and so forth of a liquid crystal compound. As an operating mode of the liquid crystal display device, such modes are known as a phase change (PC) mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a bistable twisted nematic (BTN) mode, an electrically controlled birefringence (ECB) mode, an optically compensated bend (OCB) mode, an in-plane switching (IPS) mode, a vertical alignment (VA) mode, a fringe field switching (FFS) mode and a polymer sustained alignment (PSA) mode.
Among the modes, the IPS mode, the FFS mode and the VA mode are known to allow improvement in narrowness of a viewing angle being a disadvantage of the operating mode such as the TN mode and the STN mode. In the liquid crystal display device having the mode of the kind, a liquid crystal composition having a negative dielectric anisotropy is mainly used. In order to further improve characteristics of the liquid crystal display device, the liquid crystal compound contained in the composition preferably has physical properties described in (1) to (8) below:
(1) high stability to heat, light and so forth;
(2) a high clearing point;
(3) low minimum temperature of a liquid crystal phase;
(4) small viscosity (η);
(5) suitable optical anisotropy (Δn);
(6) large negative dielectric anisotropy (Δ∈);
(7) a suitable elastic constant (K33: bend elastic constant); and
(8) excellent compatibility with other liquid crystal compounds.
An effect of the physical properties of the liquid crystal compound on the characteristics of the device is as described below. A compound having the high stability to heat, light and so forth as described in (1) increases a voltage holding ratio of the device. Thus, a service life of the device becomes long. A compound having the high clearing point as described in (2) extends a temperature range in which the device can be used. A compound having the low minimum temperature of the liquid crystal phase such as a nematic phase and a smectic phase, as described in (3), in particular, a compound having the low minimum temperature of the nematic phase, also extends the temperature range in which the device can be used. A compound having the small viscosity as described in (4) shortens a response time of the device.
A compound having the suitable optical anisotropy as described in (5) improves contrast of the device. According to a design of the device, a compound having a large optical anisotropy or small optical anisotropy, more specifically, a compound having the suitable optical anisotropy, is required. When the response time is shortened by decreasing a cell gap of the device, a compound having the large optical anisotropy is suitable. A compound having the large negative dielectric anisotropy as described in (6) decreases a threshold voltage of the device. Thus, an electric power consumption of the device is decreased.
With regard to (7), a compound having a large elastic constant shortens the response time of the device. A compound having a small elastic constant decreases the threshold voltage of the device. Therefore, the suitable elastic constant is required according to the characteristics to be desirably improved. A compound having the excellent compatibility with other liquid crystal compounds as described in (8) is preferred. The reason is that the physical properties of the composition are adjusted by mixing liquid crystal compounds having different physical properties.
A variety of liquid crystal compounds having the negative dielectric anisotropy have so far been prepared (Patent literature No. 1 and Patent literature No. 2, or Non-patent literature No. 1, for example). Patent literature No. 2 and Non-patent literature No. 1 show compound (C-1). However, compound (C-1) has no sufficiently high compatibility with other compounds.

Moreover, Patent literature No. 1 shows compound (C-2). However, compound (C-2) has no high clearing point and shows no sufficiently large negative dielectric anisotropy.

From such a circumstance, development has been desired for a compound having excellent physical properties and a suitable balance with regard to the physical properties (1) to (8) described above, in particular, for a compound having a high compatibility with other compounds and showing the large negative dielectric anisotropy.